Hisataka Hayashi

Fabrication of Silicon-on-Nothing Structure by Substrate Engineering Using the Empty-Space-in-Silicon Formation Technique

A practical method for the fabrication of a silicon on nothing (SON) structure with the desired size and shape has been developed by using the empty-space-in-silicon (ESS) formation technique. It was found that the SON structure could be precisely controlled by the initial shape and layout of the trenches. The size of ESS is determined by the size of the initial trench. The desired shapes of ESS, such as spherical, pipe-shaped and plate-shaped, can be fabricated by changing the arrangement of the initial trenches. The fabricated SON region over ESS has excellent crystallinity adoptable for ultra-large-scale integrated circuit (ULSI) applications. The SON structure would be a promising substrate structure for various manufacturing technologies, such as the micro-electro-mechanical system (MEMS), photonic crystals and waveguides.

Mechanism of Radical Control in Capacitive RF Plasma for ULSI Processing

The radicals of capacitive plasmas actually used in mass production were analyzed using various measurement systems. The composition of radicals in bulk plasma depends on the gas chemistry, the dissociation process, and interaction with the wall. It is revealed that parent gas (C4F8) is dissociated by multiple collision with electrons according to τne , where τ is the residence time, ne is the electron density, σ is the dissociation collision cross section and v is the electron velocity. A high-performance etching process, which can realize 0.09 µm contact holes with aspect ratio of 11, was achieved using a short residence time to suppress the excess dissociation and the control of deposition species through the addition of O2 to C4F8/Ar plasma as well as the reduction of the density of F radicals through the reaction with the Si wall.

Characterization of Highly Selective SiO2/Si3N4 Etching of High-Aspect-Ratio Holes

The pattern size dependence of SiO2 and Si3N4 etch rates of contact holes (RIE-lag) in C4F8+CO plasma was studied. It was found that these etch rates can be characterized by the aspect ratio, regardless of the pattern size. SiO2 etch rate decreased with increasing aspect ratio and became 0 at an aspect ratio of 6. Si3N4 etch rate also decreased; however, etching still occurred at an aspect ratio of 30. From ion current measurements through capillary plates (CPs), it was deduced that etch rates decreased because of decreasing ion current. XPS analyses revealed that fluorocarbon film deposited on the Si3N4 surface at the bottom of a hole was more F-rich than that deposited on a flat Si3N4 surface. This explained why Si3N4 is etched even in high-aspect-ratio holes. A small amount of O2 addition to the C4F8+CO plasma resolved the RIE-lag. It was found that the ion current density at high aspect ratio increased with O2 addition, which would enhance SiO2 etching and contribute to suppressing RIE-lag.

Mechanism of C4F8 dissociation in parallel-plate-type plasma

To investigate the mechanism of C4F8 dissociation in parallel-plate-type plasma, we used several of the latest diagnostic tools and made extensive measurements of electrons, radicals, and ions under conditions that greatly suppressed the effects of plasma-surface interaction. These measurements showed that the amount of light fluorocarbon radicals and ions increased with increasing electron density. The dissociation of C4F8 was analyzed by using rate equations, after confirming the stability and uniformity of the plasma. The total dissociation rate coefficient of C4F8 was 1×10−8 cm3/s, and CF2 radicals were mainly generated from products of C4F8 dissociation. F was mainly generated from CF2 by electron-impact dissociation and lost by pumping. We could estimate that the C2F4 density was roughly comparable to the densities of CF and CF3, and that the surface loss probability of C2F4 increased with increasing electron density. C2F4 might play an important role in the etching because of its rich polymerizatio...

Realistic Etch Yield of Fluorocarbon Ions in SiO2 Etch Process

The energy distribution and flux of ions striking an rf-biased electrode were measured by using an rf floating ion energy analyzer. Energies of CF1+, which was the dominant species, were distributed over a voltage range of about half the peak-to-peak bias voltage. Energetic ions with neutral radicals, forming the reactive fluorocarbon polymer layer on a SiO2 film, affected etching characteristics such as rate and selectivity. To investigate the chemical activity of the reactive layer, we estimated the etch yield of SiO2 from the given energy distribution of the ions and the etch rate of SiO2. We found that the energy dependence of the etch yield should be controlled by precisely regulating the flux and composition of neutral radicals under a given ion flux, in order to obtain a high etch rate under the actual SiO2 etching conditions.

Sub-55 nm Etch Process Using Stacked-Mask Process

Using a stacked mask process (S-MAP) with spun-on carbon (SOC) film, 56 nm line and space patterns of SiO2 were successfully etched. It was found that deformation of the SOC line pattern which occurred at line dimensions under 60 nm during SiO2 reactive ion etching (RIE) using fluorocarbon gas, originates from fluorination of the SOC film. By decreasing the hydrogen content of the SOC film, this cause of line pattern deformation was suppressed effectively.

Chemical bond modification in porous SiOCH films by H2 and H2/N2 plasmas investigated by in situ infrared reflection absorption spectroscopy

The modification of porous low-dielectric (low-k) SiOCH films by ashing plasma irradiation and subsequent exposure to air was investigated by in situ characterizations. Porous blanket SiOCH film surfaces were treated by a H2 or H2/N2 plasma in a 100-MHz capacitively coupled plasma reactor. The individual or combined effects of light, radicals, and ions generated by the plasmas on the chemical bonds in the porous SiOCH films were characterized using an in situ evaluation and by in situ Fourier-transform infrared reflection absorption spectroscopy (IR-RAS). In situ IR-RAS analysis revealed that the number of Si-OH, Si-H, and Si-NH2 bonds increased while the number of Si-CH3 bonds decreased during exposure to a H2 or H2/N2 plasma. Subsequent air exposure increased the number of Si-OH bonds by modifying Si-O-Si structures. The experimental results indicate that light emitted from a H2 or H2/N2 plasma can break Si-CH3 and Si-O-Si bonds and thereby generate dangling bonds. Radicals (e.g., NxHy and H radicals) c...

H2/N2 plasma damage on porous dielectric SiOCH film evaluated by in situ film characterization and plasma diagnostics

This study investigates the mechanism of H2/N2 plasma ashing damage of porous SiOCH films. Porous SiOCH films were treated by a H2/N2 plasma using a 100-MHz capacitively coupled plasma etcher. The impact of ions, radicals, and vacuum ultraviolet radiation on the porous SiOCH films was investigated using in situ bulk analysis techniques such as spectroscopic ellipsometry and Fourier-transform infrared spectroscopy and ex situ film characterization techniques such as dynamic secondary ion mass spectrometry and x-ray photoelectron spectroscopy. In addition, plasma analysis including vacuum ultraviolet absorption spectroscopy was performed. The film characterization and plasma analysis show that the extraction of methyl by H radicals was enhanced by light while N radicals were responsible for inhibit the extraction of Si-CH3 bonds by forming nitride layer. The H2/N2 plasma damage mechanism is discussed based on characterization of the film and plasma diagnostics.

Mechanism of Highly Selective SiO2 to Si3N4 Etching Using C4F8 + CO Magnetron Plasma

Highly selective SiO2 to Si3N4 etching was achieved using C4F8 + CO magnetron plasma when the CO gas-mixing ratio exceeded 75%. The analyses of fluorocarbon radicals in the plasma showed a higher carbon-to-fluorine ratio with increasing CO ratio. In particular, a drastic increase in the C radicals was observed, which corresponded to the increase in electron density. The reaction mechanism of CO in the C4F8 + CO plasma was investigated utilizing CO composed of the 13C isotope. CO supplied the carbon by electron-impact dissociation and scavenged fluorine by forming COFx. The carbon-implanted Si3N4 film clarified the role of carbon on Si3N4 etching. The decrease in the Si3N4 etching rate and the increase in the fluorocarbon film thickness on the surface were observed with increasing carbon dose. CO addition thus realizes the high selectivity to Si3N4 in SiO2 etching.

Sub-45 nm SiO2 Etching with Stacked-Mask Process Using High-Bias-Frequency Dual-Frequency-Superimposed RF Capacitively Coupled Plasma

By using a stacked mask process (S-MAP) with spun-on-carbon (SOC) film, 38 nm line patterns were successfully etched by controlling the ion energy using high-bias-frequency dual-frequency-superimposed (DFS) rf capacitively coupled plasma in combination with the low hydrogen content SOC film. It was found that ions with higher energy enhance the fluorination of SOC and induce pattern wiggling under fluorine exposure. By using a higher bias frequency to control the ion energy distribution and reduce the maximum ion energy, the SOC pattern wiggling was effectively suppressed.